The focus of this project is on the immunology, immunoprophylaxis, and microbiology of acute intestinal infections, viral, bacterial and parasitic. Peyer's patches are shown to be a major source of precursors of the enteric IgA response. Exposure to absorbed antigen advances the numbers and stage of differentiation of IgA precursors in Peyer's patches leading to a "more secondary" type of B-cell population. Techniques for studying the Peyer's patch precursors of IgA cells reacting with bacterial, mycoplasma and parasitic antigens have been developed. The intestinal immune response to cholera toxin/toxoid is being studied in detail, examining primary and secondary responses, dissemination of the response, memory and suppression. Simple techniques to induce and detect a vigorous mucosal antitoxic response have been developed. E. coli containing a plasmid coding for a defective LT enterotoxin have been developed as has an animal model for diarrhea due to toxigenic E. coli. These will be used to study local intestinal immunity to toxigenic E. coli. A facility for study of viral gastroenteritis has been established. Emphasis is on study of the SA-11 virus. Its antigenic properties are being compared to NCDV and a porcine rotavirus. The proteins of this virus are being purified and studied for antigenic features.